Revealing Polymorph-Specific Transduction in WO$_3$ during Acetone Sensing

TL;DR

This study investigates how different WO$_3$ polymorphs exhibit distinct electronic responses during acetone sensing, revealing that subsurface electronic states, rather than surface chemistry alone, drive transduction efficiency.

Contribution

It introduces a new perspective on gas sensing mechanisms by emphasizing the role of charge transfer energetics and electronic states in different WO$_3$ polymorphs, supported by combined experimental and theoretical analysis.

Findings

$oldsymbol{ ext{Only } ext{ε} ext{-WO}_3}$ stabilizes analyte-induced electronic states.

Both polymorphs show similar surface activation of acetone.

Deeper electronic rearrangements correlate with transduction efficiency.

Abstract

Polymorphs are distinct structural forms of the same compound and offer unique opportunities to tailor material properties without altering chemical composition. In particular, the polymorphs of WO$_3$ have been widely explored for their molecular sensing performance; yet, the mechanistic aspects behind their different chemoresistive properties have remained elusive or poorly understood. Here, we highlight the energetic allocation of transferred charge as a critical aspect for chemoresistive response generation, providing a new perspective beyond more conventional net-transfer metrics, which are usually deployed to investigate gas-solid interactions. To this, we combined operando work function, chemisorption analysis, and in situ spectroscopy with density functional theory calculations on the example of acetone. Both gamma- and $\varepsilon$-WO$_3$ exhibit comparable surface-level activation of acetone, mediated by electron-deficient, coordinatively unsaturated tungsten sites. However, only $\varepsilon$-WO$_3$ stabilizes analyte-induced electronic states derived from W(5d) orbitals lying just below the conduction band - an energetically favourable region for conductivity modulation under operating conditions. While being associated with marginal work function shifts, these states reflect deeper subsurface electronic rearrangements that may underlie the $\varepsilon$-WO$_3$'s superior transduction efficiency despite similar receptor chemistry. Our results offer a new framework for rational transducer development rooted in intrinsic electronic structure.